Hi Bojan,
I'm not sure I follow your logic here...
IR Spectrum bleed is a factor in Astrophotography irrespective of what type of telescope you use. Despite my limited experience I cannot think of a single telescope design (other than one specifically designed for IR use) that would correct for IR spectrum bleed. This would not be an issue in visual use as your eye is not capable of detecting IR spectrum without technological assistance (ie: NVG), it only becomes a factor in imaging as a sensor is sensitive enough to pickup a small amount of IR spectrum bleed, right at the end of the red end of the visual spectrum. Additionally, a sensor is sensitive enough to pickup minute quantities of the UV spectrum too, hence why regular daytime use cameras are factory fitted with a UV/IR cut filter as standard. When imaging with a camera that does not have a UV/IR cut filter, you will get small quantities of UV & IR spectrum bleed into your image which, causes star bloat & a small wash out in colours ; the only way to eliminate this is by using an UV/IR cut filter in front of the sensor..
I'm happy to be corrected but, most, if not all commercially available telescopes (other than an achromat) correct, or attempt to correct for CA in the visible light spectrum only, ie: RGB, they do not attempt to correct for UV or IR spectrum bleed at the extreme ends of the visual spectrum. I'm pretty sure the corrector plate on an SCT, no matter how high the quality does not correct for non visible light spectrum bleed..
I own a ZWO ASI224MC, the instructions specifically recommend the use of a UV/IR cut filter, I have personally seen the difference, particularly through my SCT.. no filter = star bloat, with filter = less star bloat.. not as noticeable through a refractor but, still there.. cannot comment on a newtonian but, I suspect the results would not differ...
Cheers
Quote:
Originally Posted by bojan
It is reflector system, and only element that could contribute to CA is corrector plate.
Being relatively thin. it's effect is negligeable (also according to my experince).
However, if you have other optical elements in a train (like focal reducer, field flattener) then you may need IR filter, because they may not be corrected for IR (at least cheaper models).
As to improvement you noticed with your Newt, the problem was in those additional correctors. IR filter can help there, but if you are using Newt in prime focus, IR is not needed.
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